Process for the sterilization of solid surfaces

ABSTRACT

THE STERILISATION OF SOLID SURFACES, SUCH AS THE INTERIOR OF FOOD CONTAINERS, IS ACHIEVED BY HYDROGEN CHLORIDE GAS AT TEMPERATURES BELOW 40*C. IN A MANNER SUCH THAT THERE IS NO RESIDUAL HYDROCHLORIC ACID ON THE STERILISED SURFACE, CONTROL OF THE INTERRELATED FACTORS OF TEMPERATURE, DURATION OF CONTACT, AND WATER-VAPOR, HYDROGEN CHLORIDE CONTENT BEING EMPLOYED.

United States Patent 015cc 3,576,594- Patentecl Apr. 27, 1971 US. CI.21-57 4 Claims ABSTRACT OF THE DISCLOSURE The sterilisation of solidsurfaces, such as the interior of food containers, is achieved byhydrogen chloride gas at temperatures below 40 C. in a manner such thatthere is no residual hydrochloric acid on the sterilised surface,control of the interrelated factors of temperature, duration of contact,and water-vapor, hydrogen chloride content being employed.

This invention is concerned with a method of sterilizing solid surfaces,more particularly surfaces of containers for food products,pharmaceuticals and the like, such as cans, plastic containers, glassand ceramic jars, by means of gaseous hydrogen chloride.

By sterilization we mean that substantially all living spores of aerobicand anaerobic bacteria and vegetative cells of micro-organisms arekilled.

In accordance with the invention it has been found that solid surfacescan be sterilized in a very simple and effective manner by contactingthese surfaces at ambient temperature for a certain time with anatmosphere containing an amount of gaseous hydrogen chloride andpreferably also containing an amount of water vapour, under suchconditions that after the sterilization is achieved the surface will besubstantially free of hydrochloric acid. By this we mean that in casesome hydrochloric acid is present on the surface, the amount thereof issuch that it will have no detrimental effect on the material from whichthe surface is prepared and, as the case may be, on the quality of theproduct subsequently placed in the container, so that no subsequentwashing of the surfaces is required.

The origin of the gaseous hydrogen chloride present in the atmosphere isnot an essential factor. It may be either introduced as such, forexample from a cylinder, or a product may be used which spontaneously orunder the influence of moisture will give off hydrogen chloride.Examples of such products are aluminum chloride, phosphoruspentachloride, phosphorus oxychloride and the like. However, in a verysimple and preferred embodiment of the invention aqueous solution ofhydrogen chloride is evaporated to give an atmosphere of a suitablecomposition.

It has been found that the efiicacy of the process is dependent on thefollowing factors: (a) temperature; (b) composition of the atmosphereregarding its content of hydrogen chloride and water vapour and durationof the contact, As these factors are interdependent, it is impossible toprovide absolute values for the parameters involved. However, forpractical purposes, viz. to make the process suitable for industrialuse, it is of advantage to restrict the values of the indicatedparameters to certain preferred limits as indicated below, whereby it isstated explicitly that these limits cannot be combined ad libitum andthat they are not to be construed as limiting the invention in anymanner.

Regarding the temperature it can be said that at higher temperature alower concentration of gaseous hydrogen chloride and/or a shortercontact time can be used. As indicated above the process is carried outat ambient temperature, which means a temperature of between 5 and 40C., usually of between 0 and 30 C., in particular of between 15 and 25C.

When using aqueous hydrochloric acid as source of the hydrogen chlorideand of the water vapour, the composition of the atmosphere is preferablysuch that the gaseous hydrogen chloride will exert a partial pressure (pof between 0.05 and 50 mm., preferably between 0.5 and 20 mm., whereasthe partial pressure of the water vapour (p will be between 1 and 20mm., preferably between 5 and 15 mm. These conditions can be realized byevaporating an adequate amount of aqueous hydrochloric acid of aconcentration of 10 to 37% by weight, preferably of a concentration of18 to 30% by Weight.

In case the temperature of the surface to be sterilized might be lowerthan that of its environment, care should be taken that the compositionof the atmosphere is such that the temperature of the surface is higherthan the dew point of the water vapour present in the atmosphere, asotherwise an aqueous condensate, containing hydrochloric acid, will beformed on the surface.

Finally the values of the above discussed parameters are chosen in sucha manner that an effective sterilization is achieved within 24 hours,preferably within 60 minutes.

The above indicated values are suitable for smooth surfaces. However,since it is important that the hydrogen chloride should have free accessto all parts of the surface, it is clear that the sterilization offolded surfaces, such as seams of cans, will require a longer contactand/ or higher concentration of hydrogen chloride than the sterilizationof smooth surfaces.

Furthermore it will be understood that before exposing the surfaces tothe sterilization process they will have to be cleaned and dried byconventional methods in order to remove coarse impurities. Even then thesurfaces may still be contaminated by compounds which will interferewith the sterilization process. Examples of such compounds are calciumcarbonate, fatty acids and salts thereof, oils, grease and proteins,such as milk proteins, here again depending on the amount and the typeof the adhering impurity; an effective sterilization will need a moreprolonged treatment and/or a higher concentration of hydrochloric acidyielding hydrogen chloride, which conditions can be assessedexperimentally.

The process according to the invention is particularly useful for thesterilization of inner surfaces of containers for foodstuffs, such ascans, plastic containers, glass or ceramic jars etc. in which case theprocess is conveniently applied as part of the packaging process.Furthermore the process can be employed for the sterilization of theinner surfaces of other containers, for example to be used for thepacking of bacteriological media and bacteriological cultures, for thesterilization of plastic or paper sheets, to be used for the wrapping ofmaterial susceptible to microbiological contamination and for thesterilization of surgical instruments. Finally the process can be usedfor the sterilization of surfaces of finely-divided materials, such ascrystals of kitchen salts, etc., to be used as ingredients ofpre-sterilized foodstuffs. In the latter case measures have to be takento ensure that the whole of the surface of the particles will be exposedto the hydrogen chloride-containing atmosphere. Here again the properconditions for achieving an effective sterilization can be assessed bysimple experiments,

The process is illustrated by the following examples:

3,576, 594 3 4 EXAMPLE I Glass bottles of a volume of 180 ml., wereinfected with equal amounts of the suspension and dried over-' P9?81151161190115 Were preljafed y mlxmg 10 ghyflo, night. Afterintroducing 1 drop of 30% hydrochloric acid contalmllg 105 Spores(clostrldium and 1330111115 p into each of the bottles, the latter wereclosed and kept per g. with 70 m Wate for difierent periods at atemperature of 20 C.

2 ml. of such a suspension were Spr ad evenly O e 5 The number ofsurviving moulds and Mycobacterium the inner surface of glass bottles ofa volume of 300 ml. species was determined by standard methods. Theresults After removing excess of the spore suspension by inverting aregiven in Table 3.

TABLE 3 Control After sterilization with EC] Contact time, in hr. P. g.M. r. G. s. Myc. r. Myc. p. P. g. M. r. O. s. Myc. r. Myc. p.

120 20 110 10 10 40 10 70 9x10 10 40 40 100 1. 2x10 1.1 10 0 0 10 0 s026 150 1.1 10 1. 0x10 0 0 0 o 140 33 220 111x10 1.1 10 0 0 0 0 0 50 23250 10 1. 1x10 0 0 0 0 0 70 19 220 1. 2x10 1. 2x10 0 0 0 0 0 the bottlesfor a short time, they were dried for 21 hours EXAMPLE 3 1 e at 60 to 70C. Then 0.25 ml. aqueous hydrochloric ac d Groups of 10 Internallylacquered cans (58 X 1445 was introduced into each bottle, whereafterthese bottles were sealed by means of a plastic foil. The thus treated aWidednouthed g1 ass bottle containing 25 ml 30% bottles were kept for apredetermined period at a 25 aqueous hydrochloric acid After a specifiedexposure s z gfigz s i g gi g $33 2 g g ig gz f 2?: time at 20 C. thecans were filled aseptically 'With sterile stoichiometric quantity ofsodium hydroxide. A sufficient fig f zgfifiigg i g ggfgf 8;: gif g il ay z tis a il s $2 13; gg fig ggf g i i g: fi fi, g si gi g 30 wereopened and examined for the presence of non-sporey forming andsporeformmg bacteria. after the number of surviving spores wasdetermined by The followin results were obtained conventional methods.The results are given in Tables g mm.) were placed in a plastic box of25 1., together with I and 2. Exposure time 60 minutes: out of cans notsterile TABLE I Temperature, C.

Gone. 1161 in percent" 18 24 31 37 18 24 31 37 PS0! in mm. Hg 0. 0140.18 4. 2 2o. 4 0.10 1. 0 9. 6 32 D1120 in mm. Hg 2. 86 2. 04 1. s2 1.24 11. 2 8.28 5. 55 4.

Survival 1 (Bacillus sp.)

Contact time in minutes:

5 1b l0 10.5)(10 501.0X10 14X10 60 10 10 a 10 1.1 1%3 10 10 10 1 Mean 0!3 runs.

TABLE 2 Exposure time 120 minutes: 1 out of 10 cans not sterile [Contacte: 30 u es] Exposure time 180 minutes: all cans sterile.

H% 1 i ri What is claimed is: Percent P1120 1. In a process foraseptically packaging a material in Temp.C.: containers, the improvementcomprising the steps of:

0 fig 8:2; {g3 g8 33 (i) introducing into a container an atmosphere com-30 2.12 1. 30 10 ig prising gaseous hydrogen chloride having a partial15 53 1 g 23 2 pressure of from about 0.05 to 50 mm. Hg and water 240.66 6.01 10 10 vapour having a partial pressure of from about 1 to 20is 133 if; g 33 20 mm. Hg, the inner surface of the container being 200. 228 10.2 10 10 contacted with said atmosphere being maintained 5% 3%gig $8 $8 at a temperature of from about -5 C. to 40 C., 30 1s 01 26$20. 0 10 10 said temperature being higher than the dew point of 3% 1%;2 g? the water vapour present in said atmosphere, Control 8.5 10 8. 19(ii) holding said atmosphere in contact with said inner containersurface for a period of time suflicient to EXAMPLE 2 sterilise saidsurface, and i (111) subsequently mtroducing 1nto said sterilised con-Suspensions were prepared containing 10 /ml. of the tainer said materialto be packaged. following microorganisms: Penicillium glaucum (-P.g.),2. The process according to claim 1, wherein the tem- Monascus ruber(M.r.), Cladosporium suaveolens (C.s.), perature is between 0 and 30 C.

Mycobacterium phlei (Myc.p.) and Mycobacterium ru- 3. The processaccording to claim 1, 'wherein the tembrum (Myc.r.). perature is between15 and 25 C.

References Cited UNITED STATES PATENTS Nietscke 21---58 Schmidt 2158Jackson 424---127X Hartzell et a1. 2158 Shields et a1 2157 6 FOREIGNPATENTS 5/1949 Great Britain 21-58 OTHER REFERENCES 5 Grant, 1.: HackhsChemical Dictionary; McGraw-Hill;

3rd edition; N.Y., 1944 (page 419 relied on).

MORRIS O. WOLK, Primary Examiner 10 B. S. RICHMAN, Assistant ExaminerUS. Cl. X.R. 2158; 99-182

